I’m uneasy about propane because it sinks to the low spots.
“Natural gas tends to rise into the air and scatter, whereas propane tends to collect in low-lying locations like basements, crawl spaces, and ditches.”
Natural gas wants to escape and get outside into the wind, while propane will puddle and set up an explosive environment.
Many years ago my parents bought a house in the midwest with no insulation. It had a boiler to run the radiators for the living spaces, but kerosene heaters were needed to prevent plumbing from freezing up the basement. They ditched the kerosene years ago for a gas fed heater that needs no ventilation for the basement. If the weather gets really cold they will plug in an electric heater.